Why isn't there really a Phase 2 plateau with slow current Ca2+ channels?

cells in the SA and AV nodes are not contracting muscles, their only purpose to si RAPIDLY conduct current

What are the EKG effects of hyperkalemia? (4)

bradycardia from depression of SA node activity, inexcitability of atrial cardiomyocytes leading to absence of P waves, depressed cell-to-cell depolarization of ventricles leading to depression of phase 0, large T waves due to opening of K+ channels and more rapid repolarization

What are the insulators of the atria and ventricles, and what are the chambers connected by?

cardiac valves and fibrous connective tissues are insulators; chambers are connected electrically by microscopic conduction pathway, AV node and Bundle of His

What part of the EKG lead corresponds to atrial depolarization?

P-wave

What part of the EKG corresponds with current spread across the AV node?

PQ interval

What part of the EKG lead corresponds with sequential depolarization of the ventricular myocytes?

QRS complex

What is the distribution of Ca2+ across the cell membrane?

intracellular Ca2+ is low compared to extracellular; Ca2+ does not contribute to the transmembrane potential b/c most of the intracellular C2+ is sequestered in the sarcoplasmic reticulum

What is the distribution of Na+ across the cell membrane?

intracellular Na+ is low compared to extracellular

Define an activated membrane ion channel.

once a specific ion channel is open or activated, ions can flow through the channel by their concentration gradient

Describe how the process of Na+ channels opening and depolarization occurs.

spontaneous depolarization of pacemaker cells in the SA node--> current flow across gap junctions--> depolarization of atrial and ventricular muscle cells and specialized conduction cells of the His-Purkinje system

_____________ have a prominent affect on L-type Ca2+ channels, increasing the probability of opening and Ca2+ influx; this facilitates __________ and generation of a ___________.

Catecholamines (sympathetic NS); depolarization; faster HR

High vagal tone __________ the refractory period of atrial muscle cells .

shortens

What is the purpose of the Na+K+ATPase pump?

maintain the negative intracellular potential (during phase 4) while also re-establishing the normal partitioning of ions of each side of the membrane.

Normally, the ________ is the pacemaker of the heart; the __(2)__ serve as back-up or escape pacemakers should the primary fail.

SA node; AV node and His-Purkinje cells [subsidiary pacemaker cells]

Both NE and Ach enhance ____________ and _____________ the SA nodal membrane; however, NE, the activation of the ___________ causes fuller opening of the ____________, promoting more rapid ___________; the opposite occurs with vagal Ach.

Ventricular escape beat is a self-generated electrical discharge initiated by, and causing contraction of, the ventricles of the heart; normally the heart rhythm is begun in the atria of the heart and is subsequently transmitted to the ventricles.